RNG changes (GH #593)

Change reseed interval logic to count calls to `randomize` rather than
bytes, to match SP 800-90A

Changes RNG reseeding API: there is no implicit reference to the
global entropy sources within the RNGs anymore. The entropy sources
must be supplied with the API call. Adds support for reseding directly
from another RNG (such as a system or hardware RNG).

Stateful_RNG keeps optional references to both an RNG and a set of
entropy sources. During a reseed, both sources are used if set.
These can be provided to HMAC_DRBG constructor.

For HMAC_DRBG, SP800-90A requires we output no more than 2**16 bytes
per DRBG request. We treat requests longer than that as if the caller
had instead made several sequential maximum-length requests. This
means it is possible for one or more reseeds to trigger even in the
course of generating a single (long) output (generate a 256-bit key
and use ChaCha or HKDF if this is a problem).

Adds RNG::randomize_with_ts_input which takes timestamps and uses them
as the additional_data DRBG field. Stateful_RNG overrides this to also
include the process ID and the reseed counter. AutoSeeded_RNG's
`randomize` uses this.

Officially deprecates RNG::make_rng and the Serialized_RNG construtor
which creates an AutoSeeded_RNG. With these removed, it would be
possible to perform a build with no AutoSeeded_RNG/HMAC_DRBG at all
(eg, for applications which only use the system RNG).

Tests courtesy @cordney in GH PRs #598 and #600

1 files changed, 67 insertions, 0 deletions

diff --git a/src/lib/rng/auto_rng/auto_rng.h b/src/lib/rng/auto_rng/auto_rng.h
new file mode 100644
index 000000000..6ef1aa291
--- /dev/null
+++ b/src/lib/rng/auto_rng/auto_rng.h
@@ -0,0 +1,67 @@
+/*
+* Auto Seeded RNG
+* (C) 2008,2016 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#ifndef BOTAN_AUTO_SEEDING_RNG_H__
+#define BOTAN_AUTO_SEEDING_RNG_H__
+
+#include <botan/rng.h>
+
+namespace Botan {
+
+class Stateful_RNG;
+
+/**
+* A userspace PRNG
+*/
+class BOTAN_DLL AutoSeeded_RNG final : public RandomNumberGenerator
+   {
+   public:
+      void randomize(byte out[], size_t len) override;
+
+      void randomize_with_input(byte output[], size_t output_len,
+                                const byte input[], size_t input_len) override;
+
+      bool is_seeded() const override;
+
+      void force_reseed();
+
+      size_t reseed(Entropy_Sources& srcs,
+                    size_t poll_bits = BOTAN_RNG_RESEED_POLL_BITS,
+                    std::chrono::milliseconds poll_timeout = BOTAN_RNG_RESEED_DEFAULT_TIMEOUT) override;
+
+      void add_entropy(const byte in[], size_t len) override;
+
+      std::string name() const override;
+
+      void clear() override;
+
+      /**
+      * If no RNG or entropy sources are provided to AutoSeeded_RNG, it uses the system RNG
+      * (if available) or else a default group of entropy sources (all other systems) to
+      * gather seed material.
+      */
+      AutoSeeded_RNG(size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
+
+      AutoSeeded_RNG(RandomNumberGenerator& underlying_rng,
+                     size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
+
+      AutoSeeded_RNG(Entropy_Sources& entropy_sources,
+                     size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
+
+      AutoSeeded_RNG(RandomNumberGenerator& underlying_rng,
+                     Entropy_Sources& entropy_sources,
+                     size_t reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL);
+
+      ~AutoSeeded_RNG();
+
+   private:
+      std::unique_ptr<Stateful_RNG> m_rng;
+   };
+
+}
+
+#endif